Supplemental Quarterly Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Sales and other operating revenues	$ 3,460.2	$ 3,657.6	$ 3,800.4	$ 3,116.4	$ 3,501.7	$ 3,788.0	$ 3,829.0	$ 3,244.2	$ 14,034.6	$ 14,362.9	$ 12,826.6
Income (loss) from continuing operations before income taxes	61.9	91.3	43.3	5.9	100.5	57.0	69.1	47.3	202.4	273.9	240.1
Income (loss) from continuing operations	47.6	69.2	32.7	5.3	77.5	45.0	51.8	39.3	154.8	213.6	245.3
Net income (loss)	$ 47.6	$ 69.2	$ 32.7	$ 5.3	$ 77.5	$ 45.0	$ 51.8	$ 39.3	$ 154.8	$ 213.6	$ 245.3
Income (loss) from continuing operations (per Common share)
Basic (in dollars per share)	$ 1.56	$ 2.20	$ 1.02	$ 0.16	$ 2.40	$ 1.40	$ 1.59	$ 1.17	$ 4.90	$ 6.54
Diluted (in dollars per share)	1.54	2.18	1.01	0.16	2.38	1.38	1.58	1.16	4.86	6.48
Net income (loss) (per Common share)
Basic (in dollars per share)	1.56	2.20	1.02	0.16	2.40	1.40	1.59	1.17	4.90	6.54	$ 6.85
Diluted (in dollars per share)	$ 1.54	$ 2.18	$ 1.01	$ 0.16	$ 2.38	$ 1.38	$ 1.58	$ 1.16	$ 4.86	$ 6.48	$ 6.78